Liquid crystal display panels in VA (Vertical Alignment) mode have been recently used for liquid crystal display devices such as a monitor for personal computers, and a TV, because of their wide viewing angle characteristic. Among them, practically used are liquid crystal display devices in MVA (Multi-Domain Vertical Alignment) mode in which, as an alignment control structure, one substrate is provided with electrode slits, and the other substrate is provided with projective structures to form a domain division, or liquid crystal display devices in PVA (Patterned Vertical Alignment) mode in which, as an alignment control structure, both substrates are provided with electrode slits to form a domain division.
In MVA mode and PVA mode, however, there was room for improvement in slow response speed. That is, only liquid crystal molecules near the electrode slits and the projective structures fast start to respond, even if a high voltage is applied to change black state to white state, and liquid crystal molecules far from such alignment control structures respond late.
For improvement of the response speed, it is effective that alignment films provided on liquid crystal layer side surfaces of substrates are subjected to an alignment treatment, whereby to provide liquid crystal molecules with pretilt angles previously. Also in VA mode, liquid crystal molecules are previously made slightly incline toward vertical alignment films, and thereby can easily incline when a voltage is applied to the liquid crystal layer. Therefore, the response speed can be made faster. A rubbing method, a SiOx oblique deposition method, and a photo-alignment method may be mentioned as methods of the alignment treatment for providing liquid crystal molecules with the pretilt angles.
The domain division is performed to obtain a wide viewing angle in MVA mode and PVA mode. However, the domain division in MVA mode and PVA mode has room for improvement in that more alignment treatment steps are needed for alignment films. For example, as the rubbing method, a method, in which a region to be rubbed and a region not to be rubbed are separated using a resist pattern to be subjected to a rubbing, has been proposed. As the photo-alignment method, a method, in which one or more times of exposures via a photomask is performed for the domain division, has been proposed. It is desirable that the number of times of such an alignment treatment is fewer in terms of simplification of production steps. However, one pixel has preferably two or more domains, and most preferably four or more domains in order to secure a wide viewing angle. Therefore, a method, in which many domains can be secured by fewer times of alignment treatments, has been needed.
As VA mode in which the domain division is performed, proposed has been VA mode (hereinafter, also referred to as VAECB (Vertical Alignment Electrically Controled Birefringence) mode) using vertical alignment films, in which alignment directions on each other's substrates are antiparallel in any domain, as shown in FIGS. 11A, 11B, 12-1 and 12-2. In VAECB mode, as shown in FIG. 12-1, a direction of an absorption axis of a first polarizer 5 formed on a first substrate side and a direction of an absorption axis of a second polarizer 6 formed on a second substrate side are out of alignment with an alignment direction of a first alignment film 1A and an alignment direction of second alignment direction 2A by 45 degrees. In a mode for dividing one pixel into four domains, which is particularly excellent in viewing angle in VAECB mode, throughput in volume production decreases since the alignment treatment is performed in four directions, i.e. 45, 135, 225, and 315 degrees, as shown in FIG. 12-2. For example, Japanese Kokai Publication No. 2001-281669 discloses a technique, in which an alignment treatment is performed by a photo-alignment method to provide VAECB mode, but this technique needs a total of eight times of exposure processes for the alignment films.
On the other hand, VAHAN (Vertical Alignment Hybrid-aligned Nematic) mode in which one substrate is provided with a vertical alignment film not subjected to an alignment treatment, can decrease the number of times of the alignment treatment. However, there is room for improvement in response speed since a pretilt angle of liquid crystal molecules remains 90 degrees on the one substrate side.
With this problem, proposed has been VA mode (hereinafter, also referred to as VATN (Vertical Alignment Twisted Nematic) mode) using vertical alignment films, in which alignment treatment directions on each other's substrates are perpendicular to each other to make liquid crystal molecules form a twist structure (for example, with reference to Japanese Kokai Publication No. Hei-11-352486, Japanese Kokai Publication No. 2002-277877, Japanese Kokai Publication No. Hei-11-133429, and Japanese Kokai Publication No. Hei-10-123576). In VATN mode, a direction of an absorption axis of a first polarizer and an alignment direction of a first alignment film are the same, and a direction of an absorption axis of a second polarizer and an alignment direction of a second alignment film are the same. Alternatively, the direction of the absorption axis of the first polarizer and the alignment direction of the second alignment film may be the same, and the direction of the absorption axis of the second polarizer and the alignment direction of the first alignment film may be the same. A mode, in which one pixel is divided into four domains in VATN mode, needs only four times of alignment treatments, which is half the number of times in VAECB mode.
Such VATN mode is theoretically excellent in that fewer times of processes can provide a wide viewing angle and high-speed response. However, a technique for producing a liquid crystal display device in VATN mode has not been established yet. There is room for improvement in display brightness characteristic and the like.